为什么Java中的Calendar在Java和Android下结果不一样

在java 环境下打运行
Calendar c=Calendar.getInstance();
c.setFirstDayOfWeek(Calendar.MONDAY);
System.out.println(c);
System.out.println(c.get(Calendar.WEEK_OF_YEAR));

打印结果，周数48是对的
java.util.GregorianCalendar[time=1385876708339,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zOne=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitiOns=19,lastRule=null],firstDayOfWeek=2,minimalDaysInFirstWeek=1,ERA=1,YEAR=2013,MOnTH=11,WEEK_OF_YEAR=48,WEEK_OF_MOnTH=1,DAY_OF_MOnTH=1,DAY_OF_YEAR=335,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MOnTH=1,AM_PM=1,HOUR=1,HOUR_OF_DAY=13,MINUTE=45,SECOnD=8,MILLISECOnD=339,ZONE_OFFSET=28800000,DST_OFFSET=0]
48

但是同样的代码在android环境下就成了这样 周数变成了49
java.util.GregorianCalendar[time=1385876864988,areFieldsSet=true,lenient=true,zOne=Asia/Shanghai,firstDayOfWeek=2,minimalDaysInFirstWeek=1,ERA=1,YEAR=2013,MOnTH=11,WEEK_OF_YEAR=49,WEEK_OF_MOnTH=1,DAY_OF_MOnTH=1,DAY_OF_YEAR=335,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MOnTH=1,AM_PM=1,HOUR=1,HOUR_OF_DAY=13,MINUTE=47,SECOnD=44,MILLISECOnD=988,ZONE_OFFSET=28800000,DST_OFFSET=0]
49

不知道是什么原因，求解释